The invention is directed to a cleaning agent for glass ceramic surfaces containing a quantity of abrasive and having a pH value of less than 6.
Glass ceramic materials are polycrystalline solids made by the ceramification, i.e., controlled devitrification, of glasses. Glass ceramic products are shaped by glass technology processes and after heat treatment possess the properties and processability of special ceramics, in particular a very high capacity to withstand temperature fluctuations. This latter property makes them particularly suitable for cooker hob and crockery applications, for which they have been used to an increasing degree in recent years.
Especially in cooker hob applications, glass ceramic is exposed to a specific type of dirt which includes, in addition to proteins, starch and fat (e.g., cooking sauce, tomato puree, milk, noodles, rice or potatoes), and calcium stains, especially in regions where the water is particularly hard.
The usual approach to removing stains of this type is to use acid cleansers containing abrasives, such as mixtures of clay earth of differing particle sizes as described in European published patent application EP 0 388 629 A1, for example. All commercially available cleaning agents for glass ceramic surfaces contain abrasives in the form of water-insoluble minerals with a typical Mohs hardness of between 7 and 9. Although very effective, these abrasives attack the surfaces to be cleaned, in many instances because of their hardness. This quite rapidly leads to unsightly, i.e., scratched, surfaces, especially in the case of glass ceramic.
Plastics have long been used as abrasive agents in body cleansing agents, especially in cleansers for the hands, in order to provide a gentler, more skin-friendly alternative to the harsh scouring effect of mineral abrasives.
U.S. Pat. No. 3,645,904 proposes the use of synthetic resin particles for skin cleaning preparations. Mention is made, among other things, of polyolefins, which are relatively soft, in particular polyethylene, polypropylene and polystyrene. The particles have a diameter of 74 to 420 xcexcm and the quantity used in the product is 3 to 15% by weight.
German Patent DE 16 69 094 D2 discloses cleaning agents with 100 parts of liquid soap and 10 to 900 parts of polyethylene-abrasive agent with a particle size of 10 to 1000 xcexcm. The compositions are described as being suitable for cleaning hands and for gentle cleaning of hard surfaces, in particular lacquered metal.
Japanese published examined application 06-033414 B2 discloses the use of 5 to 30% by weight of organic abrasive with a particle size of from 10 to 500 xcexcm in body washes and for removing rust or carbon deposits from machinery. Polyurethane and polyolefins are among other abrasives described. The minimum content of abrasive needed to produce an effective action is 5% according to this prior art document.
Abrasives made from plastics are also mentioned in connection with domestic cleaning agents, usually to provide a gentle cleaning action on sensitive surfaces.
European published patent application EP 0 011 984 A1 discloses liquid alkaline cleansing agents containing water-insoluble multivalent metal soaps as a means of imparting thixotropic qualities and stability to the formulations. Ground polymer materials, such as ground polyurethane foam, are cited as abrasives. However, mineral abrasives are preferred.
European published patent application EP 0 030 986 A1 discloses a liquid washing-up detergent, having a pH value of from 6 to 11 and containing surfactants, builders and 3 to 20% of abrasives with a Mohs hardness of from 2 to 7 and a particle size of from 1 to 150 xcexcm. Both inorganic and plastic materials, e.g., polystyrene and polyacrylates, are disclosed as abrasives. However, no specific example is given for the use of plastic abrasives.
European published patent application EP 0 206 534 A1 discloses liquid alkaline cleaning agents which incorporate a thickening system consisting of an inorganic colloid and an anionic fatty acid surfactant. Inorganic materials are specifically disclosed as abrasives, although organic materials are briefly mentioned.
European published patent application EP 0 216 416 A2 discloses a liquid cleaning agent containing 1 to 50% by weight of a water-soluble mild abrasive, mention being made of both inorganic and organic materials. If using organic materials, the preferred range is 5 to 15% by weight. The preferred abrasive, and in fact the only one documented in the examples, is calcium carbonate.
European published patent application EP 0 335 471 A1 discloses a cream cleansing agent containing 10 to 60% by weight of an abrasive agent. Inorganic and organic abrasives are mentioned and, in the case of applications using organic abrasive, particular mention is made of the fact that the latter reduces scratching on sensitive surfaces, for example made from plastic. The only abrasive mentioned and the one documented in the examples, however, is calcite.
International application publication WO97/47724 A1 discloses a liquid cleaning agent in liquid crystal form, which contains up to 20% by weight of abrasive selected from the group consisting of hydrated silica, calcite and polyethylene particles with a particle size of 200 to 500 xcexcm. No reasons are given as to why this abrasive should be selected.
Although it is evident from the state of the art that abrasives made from plastics may be used if a gentler scouring action than that obtained with mineral abrasives is desired, e.g., to protect sensitive surfaces, no details are given as to the cleansing effect of abrasives of this type, especially in comparison with mineral abrasives. Moreover, no acid cleaning agent is known which contains an abrasive made from plastic.
Accordingly, an underlying objective of the invention is to propose a cleaning agent of the generic type with an improved cleaning action. This objective is achieved by the invention in the form of a cleaning agent for glass ceramic surfaces, containing a quantity of abrasive agent and having a pH value of less than about 6, in which the abrasive agent comprises particles of an organic material. This being the case, the abrasive preferably comprises at least about 20% by weight, more preferably substantially entirely, organic material.
The content of abrasive agent in the cleaning agent proposed by the invention is preferably about 10% by weight or less, more preferably about 5% by weight or less. Preferred organic polymers are polyolefins, such as polyethylene, or polyurethane. Preferably, the organic material is present in a particle size (diameter or largest dimension) within a range of about 10 to 1000 xcexcm, more preferably about 100 to 200 xcexcm.
The invention is additionally directed to the use of an organic material, alone or in combination with a mineral compound, as an abrasive in a cleaning agent for glass ceramic surfaces in order to improve the cleaning action.
Totally surprisingly, it has been found that acid cleaning agents exhibit a superior cleaning action on glass ceramic surfaces, such as glass ceramic cooker hobs, if the usual mineral abrasive is partially or totally replaced by an abrasive made from organic material. Even more surprising was the cleaning performance, given that, even with a low content of abrasives of less than about 10% by weight, the cleaning action was superior to that of standard commercial cleaning agents containing mineral abrasives in a quantity of, for example, 26% by weight. As an additional advantage, as expected, the lower hardness and larger particle size of the organic abrasive proved to be much kinder to surfaces.
The organic material, which partially or entirely comprises the abrasive agent, may be varied in nature. Consideration may be given in particular to synthetic organic polymers, for example polyurethane, polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, ABS resin, urea resin, polycarbonates, polyamides, phenolic resins, and epoxy resins. Of these, polyurethane and polyethylene are more particularly preferred. In addition, however, organic materials of natural origin may be considered, such as rice husks, ground corn cobs, ground walnut shells, etc. The particle size of the organic material is preferably about 100 to 200 xcexcm, but may also be smaller (down to 10 xcexcm) or larger (up to 1000 xcexcm).
If the organic material is used in conjunction with inorganic abrasives (the ratio in such a mixture not being particularly critical, although it is preferable to use a proportion of at least about 20% by weight of organic material), the inorganic abrasives may be selected from the whole range of mineral abrasives mentioned above, such as aluminium oxide, silicon dioxide, sillitin, boehmite, hydrargillite, aluminium silicate, kaolinite, etc.
Other important functional ingredients of the cleaning agent proposed by the invention are surfactants. Of these, essentially all known surfactants which are compatible with an acid medium may be considered, i.e., non-ionic surfactants, such as the entire range of fatty alcohol ethoxylates or alkyl ethoxylates; amphoteric surfactants, such as amido-betaines, betaines, alkylamino-carboxylates, imino-diproprionates, etc.; anionic surfactants, such as alkyl sulphates, alkyl ether sulphates, sulpho-succinates, etc.; and cationic surfactants, such as protonated alkyl amines, ethoxylated alkyl amines, etc.
Another important ingredient is acid or an acid mixture, preferably selected from organic acids, such as citric acid, amido-sulphuric acid, glycolic acid, lactic acid, etc. The preferred pH value for the cleaning agent is about 2 to 5, more preferably about 2 to 3.
Other ingredients which may be incorporated in the cleaning agent proposed by the invention include solvents, such as isopropyl alcohol, polyethylene glycol, N-methyl-2-pyrrolidone, etc.; thickening agents, such as xanthan gum or organic-modified silicates (e.g., OPTIGEL(copyright)WX); care-enhancing additives, such as polydimethyl siloxane (with a viscosity of about 100 mPas to 12,500 mPas), organo modified silicones, amino-functionalized silicones, silicon quats, polyvinyl pyrrolidones, etc; fragrances, dyes; preservatives, etc.
Further details of the tests that were conducted are set out in the example below.